A node that performs a manual switching command clears the manual switching command after receiving the Clear command. A node
keeps blocking the ring network port blocked by the previous manual switching command and continuously sends NR messages to both
ring network ports. and the following link recovery, the behavior and function of return mode and non-return mode are inconsistent.
1.4.5.1 Return Mode
In return mode, the ring link is restored. RPL node receives the NR message and starts the WTB timer. WTB the timer timeout, the RPL
node blocks the link, sends NR RB messages, and Flush FDB. them The rest of the ring network nodes unblock all non RPL links after
receiving the NR RB message, and then Flush FDB.
1.4.5.2 Non-return Mode
In non-return mode, the ring link does not automatically recover. RPL node does not reply after receiving the NR message, and the other
nodes do not do any action after receiving the NR message. Only when RPL node receives the Clear command will the RPL node block the
link and continuously send NR RB messages to the two ring network ports, then Flush FDB.The rest of the ring network nodes unblock all
non RPL links after receiving the NR RB message, and then Flush FDB.
1.4.6 Protection Switching —— Forced Switching
When a loop network node receives a forced switching command, it blocks the data channel and R-APS channel (blocking the port of one
data channel and R-APS channel), opens the other loop network ports, and continuously sends FS messages to the two loop network
ports, then Flush FDB.. The remaining ring network nodes receive FS messages and open the data flow and R-APS channels through the
RPL. The ring network node that sends FS message stops sending FS message after receiving the message. Network nodes perform FDB
Flush. after receiving FS message
The above actions completed a forced switching operation, in order to normal switching, there is a point to note:
When a forced switching command already exists in the ring network, subsequent forced switching requests are accepted unless the
node has previously accepted a forced switching request. At the same time, the node receiving the new switching command to
re-enforce switching operation, blocking ports, sending FS messages and so on. Of course, the execution of multiple forced switching
commands will split the ring network, so it should be properly avoided.
A node that performs a mandatory switching command clears the mandatory switching command after receiving the Clear command. A
node keeps blocking the ring network port blocked by the previous forced switching command and continuously sends NR messages to
both ring network ports. and the following link recovery, the behavior and function of return mode and non-return mode are
inconsistent.
1.4.6.1 Return Mode
In return mode, the ring link is restored. RPL node receives the NR message and starts the WTB timer. WTB the timer timeout, the RPL
node blocks the link, sends NR RB messages, and Flush FDB. them The rest of the ring network nodes unblock all non RPL links after
receiving the NR RB message, and then Flush FDB.
1.4.6.2 Non-return Mode
In non-return mode, the ring link does not automatically recover. RPL node does not reply after receiving the NR message, and the other
nodes do not do any action after receiving the NR message. Only when RPL node receives the Clear command will the RPL node block the
link and continuously send NR RB messages to the two ring network ports, then Flush FDB.The rest of the ring network nodes unblock all
non RPL links after receiving the NR RB message, and then Flush FDB.
1.4.7 Replacement Recovery Process
The ring network protection node (RPL Owner) realizes the ring network switching recovery through timer WTR (wait-to-restore timer)
and timer WTB (wait-to-block timer).WTR timer and WTB timer are used to avoid frequent protection switching on the ring network.
WTR timer only takes effect in return mode, in non-return mode, when the ring network is recovered from the protection state, the ring
network recovery is not carried out, so there is no need to turn on the WTR timer. while in return mode, after RPL node receives NR
messages from other nodes, the WTR timer is started. before the timer time-out, the RPL node maintains the forwarding state of the port
and does not send a ring network recovery notification. When RPL node receives SF message again, it indicates that the ring network has
not been fully restored, and the node stops WTR timer.WTR the RPL node re-blocking the port after the timer timeout.
WTB timer only works in return mode, used when clearing forced and manual switching commands. When you clear multiple forced
switching commands, the WTB timer ensures that a single forced switching command does not cause RPL to duplicate blocking. When a
manual switching command is cleared, the WTB timer prevents the RPL node from receiving a closed loop caused by an outdated remote
MS request during recovery.
The WTB timer must ensure that there is enough time to receive remote FS、SF and MS messages, so defining the WTB timer is 5 seconds
longer than the Guard timer, which is enough for a reporting ring node to send two R-APS messages and allow the entire ring network to
confirm situation.
5
www.fs.com
S3400-48T4SP SWITCH ERPS CONFIGURATION GUIDE